This invention relates to the synthesis of polymers from polyfunctional monomers, and more particularly to the synthesis of branched polyureas, polyurethanes, polyamidoamines, polyamides and polyesters.
Polyureas, polyurethanes, polyamidoamines, polyamides and polyesters are typically synthesized from difunctional monomers to produce linear polymers, or from a combination of difunctional and polyfunctional monomers to prepare thermoset resins. Thermoplastic and thermoset polyureas, polyurethanes polyamidoamines, polyamides and polyesters have exhibited utility in a variety of applications. However, there is a recognized need for branched, and more particularly for highly branched, thermoplastic polymers. It is now recognized that chemically similar polymers having different molecular architectures can exhibit different properties and advantages. For example, polymer-coating compositions comprising a highly branched polyester have a lower viscosity and better shear thinning properties for coating applications than similar compositions containing a chemically similar linear polyester having the same molecular weight and same concentration.
One method of synthesizing branched polymers is to use polyfunctional monomers (i.e., monomers having three or more functional groups) during polymerization. However, this method may result in the production of gelled or thermoset cross-linked materials that do not exhibit good processability characteristics, and which are insoluble.
It has been suggested that dendrimers can be employed in certain applications to achieve improved properties, such as thermoplastic processing characteristics, lower viscosity, and improved rheology, as compared with linear polymers having similar chemistry and molecular weight. However, dendrimers are monodisperse (typically having a polydispersity of less than about 1.02), highly defined molecules that are prepared by a series of controlled stepwise growth reactions which generally involve protect-deprotect strategies and purification procedures at the conclusion of each step. As a consequence, synthesis of dendrimers is a tedious and expensive process that places a practical limitation on their applicability.
In contrast to dendrimers, hyperbranched polymers are prepared in a one-step, one-pot procedure. This facilitates the synthesis of large quantities of materials, at high yields, and at a relatively low cost. Although the properties of hyperbranched polymers are different from those of dendrimers due to imperfect branching and larger polydispersities, hyperbranched polymers exhibit a degree of branching intermediate between that of linear polymers and dendrimers, and, therefore, exhibit thermoplastic processing and rheological properties that are comparable or for some applications superior to those of dendrimers. Accordingly, hyperbranched polymers have been perceived as being useful in certain applications as a lower cost alternative to dendrimers.
Heretofore, hyperbranched polymers, including hyperbranched polyureas, polyurethanes, polyamidoamines, polyamides and polyesters, have been prepared using a monomer having at least one functionality of one type (A), and at least two functionalities of another type (B), wherein functionalities of the same type are not reactive with each other, and functionalities of the first type are reactive with functionalities of the second type to form hyperbranched polymers via condensation or addition reactions. The monomers employed during synthesis of conventional hyperbranched polymers are designated as AxBy monomers, wherein A represents a functional group of a first type that does not react with itself, B represents a functional group of a second type that does not react with itself but reacts with the functional groups of the first type, x is at least 1, and y is at least 2. However, there are relatively few commercially available AxBy monomers, and synthesis of such monomers is generally more difficult than synthesis of monomers having a single type of functionality. As a result, the variety of hyperbranched polymers that can be synthesized from AxBy monomers is limited and, although they are generally less expensive than dendrimers, they are often too expensive for many applications.
This invention provides hyperbranched polyureas, polyurethanes, polyamidoamines, polyamides and/or polyesters prepared from difunctional and/or polyfunctional monomers having functional groups of one type (A) without any other functional groups that react significantly during the polymerization process, and difunctional and/or polyfunctional monomers having functional groups of another type (B) that react with a functional groups of the first type (A) without any other functional groups that react significantly during the polymerization process. More specifically, the hyperbranched copolymers of this invention are prepared by a process in which a monomer having the form Ax is reacted with another monomer of the form By, where A is a functional group that does not react with itself during the polymerization process, B is a functional group that does not react with itself during the polymerization process but participates in an addition or condensation reaction with a first functional group (A) to form a hyperbranched copolymer, x and y are integers which each have a value of at least 2, and at least one of x and y is an integer having a value of at least 3.
The process of this invention enables synthesis of hyperbranched polyureas, polyurethanes, polyamidoamines, polyamides and/or polyesters from comonomers, each of which has a single type of functional group, thereby providing greater flexibility in the preparation of a larger variety of different hyperbranched polyureas, polyurethanes, polyamidoamines, polyamides and/or polyesters. Because Ax and By type monomers are easier to synthesize than AxBy type monomers, the process of this invention also enables hyperbranched polyureas, polyurethanes, and/or polyesters to be prepared at a lower cost than conventional synthesis processes.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification and claims.